In recent years, silicone hydrogel has been proposed as a material for contact lenses. Silicone hydrogel is excellent in terms of oxygen permeability compared to the hydrogel of the prior art, so it is being studied for use with soft contact lenses.
Soft contact lenses are provided to users in a state immersed in a storage solution, sealed in the contact lens package, and shipped to the market. At that time, the time from when the contact lens package is provided to the market by the manufacturer until the lenses are worn by the user can take a long time, from several weeks to several years. Over such a long time, the soft contact lenses need to have stable preservation of their physical properties and shape. In particular, it is necessary not only to satisfy the product specifications, but also to maintain high precision since changes in shape bring changes in the wearing comfort or optical characteristics for the user. In light of that, methods for storing soft contact lenses include for example the methods noted in Patent Document 1 (Japanese National Phase of PCT Application Publication No. JP-A-2004-517163) and Patent Document 2 (Japanese National Phase of PCT Application Publication No. JP-A-2000-513665).
However, upon checking by the inventors, with silicone hydrogel soft contact lenses, the inventors found that it is difficult to sufficiently ensure the dimensional precision of the lens diameter (DIA) and the like. For this dimensional precision problem, initially efforts were made to improve the molding precision, but it was difficult to obtain satisfactory results with that. In light of that, upon further examination by the inventors, it was newly discovered that this is a problem specific to silicone hydrogel soft contact lenses, and that the lens shape (dimension) changes under hermitically sealed storage conditions after the contact lenses are manufactured.